Having NPC allies instead of enemies could be interesting under any circumstances. Maybe you could finally give Cayde what he wants and take him along with you. Or, you could assist the Sunbreaker titans; like the Awoken they have no allegiance to the City but they and you might share a common goal. Or consider this: one of Destiny's most annoying aspects is that the Darkness and its minions (Vex, Taken, Hive) are intent on the destruction of humanity, but they are also an enemy to the Fallen and the Cabal. Despite being surrounded by a nearly all-powerful force that seeks our mutual annihilation, we still insist on shooting at each other. Maybe there could be missions where these races temporarily set aside their own disagreements in the face of a mutual threat. You could have Vandals or Captains fighting at your side, or a row of allied Phalanxes to hide behind while your shields recharge.